The sequence of events culminating in a renal calculus of clinically significant size remains to be established. Our work with thorough clinical, endoscopic, metabolic, and histologic examination of stone formers (SF) suggests that specific physiologic events in the kidney result in characteristic patterns of crystal deposition and eventual stones. Aim 1 will extend our work, which began with the confirmation and elaboration of the work of Randall in common calcium oxalate SF and is extending to include other crystal deposits and stone phenotypes. In Aim 2 we hypothesize that rigorous examination of common calcium oxalate SF undergoing endoscopic stone removal will demonstrate either stone attached to plaque or evidence of plaque in any non-attached stones. As with Aim 1, the protocol of Aim 2 will be extended to other stone phenotypes. With the development of multi-detector CT technology, non-invasive visualization of Randall's plaque (RP) is now possible. Using our now well established endoscopic mapping techniques as a standard, Aim 3 will attempt to define and quantitate CT plaque characteristics and will investigate radiographic criteria for distinguishing RP from stone. Finally, Aim 4 will explore the relationship of urinary stasis to stone formation, a topic that heretofore has not been subjected to rigorous science. Two models (calyceal diverticula, ureteropelvic junction obstruction) will be utilized in this Aim.